The present invention relates to a digital vertical synchronization system for use in a television receiver set or the like, wherein a vertical synchronizing signal separated from a composite synchronizing signal is synchronized with a vertical deflection control signal obtained by counting clock pulses which are synchronized with a horizontal synchronizing signal separated from the composite synchronizing signal.
There have hitherto been proposed digital processing methods of horizontal and vertical synchronization systems in a television receiver set or the like.
In a digital vertical synchronization system of the prior art, a clock pulse having a frequency equal to, for example, twice that of a horizontal synchronization frequency is applied to a clock counter having T-type flip-flops which are connected in cascade, so that a vertical deflection control signal with a pulse width of 6.5H (where H denotes one horizontal scanning period) is produced at every given vertical scanning period. The phase of this vertical deflection control signal is compared with the phase of a vertical synchronizing signal with a pulse width of 3H separated from the composite synchronizing signal by a CR integrator. If these phases are not coincident, the clock counter is reset to make the phases coincide.
The vertical deflection control signal with the pulse width of 6.5H derived from the clock counter, however, has a larger pulse width in comparison with the vertical synchronizing signal with the pulse width of 3H separated from the composite synchronizing signal. As a result, if the repetition cycles of the vertical deflection control signal and vertical synchronizing signal are different slightly from each other, it takes a long time to detect the difference of those repetition cycles by a phase comparator and to reset the clock counter for making these phases coincide. This long time to detect the repetition cycles difference and to reset the clock counter causes a distorted appearance, and a small vibration, so-called jitter, in the reproduced picture on the screen of the television receiver set or the like.